This invention relates to wireless communications, and more particularly to code division multiple access (CDMA) wireless communications.
Wireless communication provides tetherless access to mobile users and addresses the requirements of two specific and disjoint domains: voice telephony and indoor data LANs. Cellular telephone networks have extended the domain of telephone service over a wireless last hop, while mobile-IP LANs such as WaveLAN and RangeLAN do the same for indoor users of TCP/IP data networks. Advances with wireless technology and high-speed integrated service wired networking promises to provide mobile users with comprehensive multimedia information access in the near future. For example, Personal Communication Services (PCS) are a broad range of individualized telecommunication services which enable individuals or devices to communicate irrespective of where they are at anytime. Personal Communication Networks (PCN) are a new type of wireless telephone system communicating via low-power antennas. PCNs offer a digital wireless alternative to the traditional wired line.
The following represent areas of concern in wireless technology, for example, in any wireless communication system, transmitter power has an important impact on system performance. In a noise limited wireless communication system, the transmitted power determines the allowable separation between the transmitter and receiver. The available transmitted power determines the signal-to-noise ratio, which must exceed some prescribed threshold at the receiver input for successful communication of information to occur.
When transmitting a message signal over a communication channel, both analog and digital transmission methods can be used. Digital methods are preferred due to advantages over analog methods, including: increased immunity to channel noise and interference; flexible operation of the system; common format for the transmission of different kinds of message signals; improved security of communications through the use of digital encryption; and increased capacity.
Efficient utilization of bandwidth is another concern. One means of accomplishing effective utilization of available bandwidth is through signal multiplexing, in which signals from several message sources are simultaneously transmitted over a common spectral resource. Frequency division multiplex, time division multiplex, and mixtures have been used for implementing signal multiplexed cellular radio systems.
Another multiple access system involves the use of wideband communications, as opposed to narrowband approaches like frequency division multiple access (FDMA) and time division multiple access (TDMA). In cellular radiotelephone systems such wideband communications have been achieved using code division multiple access (CDMA) spread spectrum techniques. Such spread spectrum systems utilize a modulation technique for spreading the information being communicated over a wide frequency band. This frequency band is typically much wider than the minimum bandwidth required to transmit the information being sent.
In a direct sequence CDMA system, communication between two communication units is accomplished by spreading each transmitted signal over a wide frequency band with a unique user spreading code. This results in a plurality of transmitted signals sharing the same frequency. The ability of such a system to work is based on the fact that each signal is specially time and/or frequency coded to permit its separation and reconstruction at the receiver. Particular transmitted signals are retrieved from the communication channel by despreading a signal from all of the signals by using a known user spreading code related to the spreading implemented at the transmitter.
There is a significant investment in spectrum resources and equipment currently supporting narrowband CDMA. When a wideband CDMA (W-CDMA) system which utilizes several carriers is overlaid on IS-95 carrier(s) there is a capacity loss. In general, any unbalanced interference and unbalanced loading across carriers will degrade the aggregate capacity.
The present invention is a method for allocating utilization of multiple carriers in a wideband CDMA transmission system. The method first determines the carrier utilization/interference levels for each of the multiple carriers. Based on the carrier utilization/interference level, carrier assignments are allocated on an unequal basis. The allocation of the carrier assignment biases the selection of the carriers away from higher utilized/interfered carriers. An apparatus for implementing the method is also described.